1. Field of the Invention
This invention relates a magnetic recording disk cartridge comprising a casing and a magnetic recording disk accommodated therein for rotation, and more particularly to an improvement in cleaning means for the magnetic recording disk.
2. Description of the Prior Art
There has come into wide use as a recording medium for computers a floppy disk which is a flexible disk of polyester resin or the like bearing a magnetic layer on each side thereof and on which digital information is recorded by a magnetic head while the recording disk is rotated.
Recently, there has been proposed a so-called electronic camera in which, instead of a conventional silver salt photographic film which cannot be reused, a magnetic recording disk which is smaller than the floppy disk both in thickness and diameter and is generally referred to as "a micro floppy disk" is used as a recording medium. Generally the micro floppy disk for the electronic camera is accommodated in a hard casing to form a cartridge. The micro floppy disk comprises a circular magnetic recording medium which is small in diameter and is extremely thin, and a hub fixed to the center of the recording medium. The hard casing has a hub opening through which the hub is exposed and a magnetic head receiving opening formed in at least one side wall thereof.
The magnetic recording disk cartridges including the floppy disk and the micro floppy disk are generally provided with a liner on the inner surface of the casing. The liner is formed of unwoven fabric of a textile blend of rayon and polyester, for instance, and is kept in contact with the recording surface of the recording disk under a light pressure to remove dust on the recording surface while the recording disk is rotated. The liner has a width at least equal to the width of the recording region of the magnetic recording disk, and is pressed against the recording surface under a uniform pressure over the entire width thereof. However, since the amount of information recorded during one rotation of the disk does not differ between the outer part and the inner part of the recording region and the linear velocity is smaller in the inner part than in the outer part, the recording wavelength is shorter in the inner part of the recording region than in the outer part of the recording region. Therefore, even fine dust which could give rise to hardly any problem on the outer part of the recording region can cause drop-out and the like when it is deposited on the inner part of the recording region. Accordingly, when the liner is pressed against the recording surface under a uniform pressure required to clean the recording surface to an extent enough for the outer part of the recording region, the inner part of the recording region cannot be cleaned enough. On the other hand, when the liner is pressed against the recording surface under a higher uniform pressure, the running torque of the recording disk or the torque required to rotate the recording disk is increased, which is practically undesirable.